Heating hydrocarbon fluid



Patented July 15, 1941 EEEQE.

HEATING HYDROCARBON FLUKE) John Herman Ric'kcrman, River Edge, N. J.,assignor to Gasoline Products Company,'lnc., Jersey City, N. J., acorporation of Delaware Application October 14, 1939, Serial No. 299,536

3 Claims.

This invention relates to heating apparatus adapted for heatingfluidsandmore particularly relates to heating hydrocarbon fluids to conversiontemperature.

In the conversion of hydrocarbon fluids for the production of motor fuelit is desired to quicldy raise the temperature of the hydrocarbon fluidas it, passes through the furnace or heating apparatus to quicklyapproach. the conversion temperature. At thisstage of the heating thedan ger of carbon or. coke deposition in the heater tubes or coil isrelatively small and large amounts of heat may be added per unit ofheating surface or the rate of heating of the hydrocarbon fluid may berelatively high. After the hydrocarbon fluid has reached a conversiontemperature the rate of heating of the hydrocarbon fluid must bedecreased and controlled to minimize carbon deposition and cokeformation in the heater tubes, but suflicient heat must be added perunit of heating surface to effect the desired extent .of conversion.

, According to my invention heater tubes are so arranged and spaced in aradiant heating section of a heating apparatus to control the heating ofthe hydrocarbon'fluid passing through the heater tubes. I have shown abox-type furnace as a specific form of my invention in which the furnaceis provided with a radiant heating section and a convection section, theradiant heating section being provided with heater-tubes extendinglongitudinally of the furnace. The heater tubes are interconnected toform a heater coil or continuous passage for the hydrocarbon fluid. Inthe specific form of apparatus shown in the drawing there are includedcommunicating radiant heating sections preferably heated by combustionof fuel and a common overhead convection section for receivingcombustion products from the radiant heating sections. The inventionisnot to be limited to this showing as a single radiant heating sectionand a single convection section may be used. My invention may also beused with other types of furnaces. The radiant heating sections as shownare substantial duplicates and separate streams are preferably passedthrough the separate radiant heating sections.

The heating of one of these streams will now be described briefly.Hydrocarbon fluid to be heated is passed through heater tubes in acommon convection heating section and is then passed through heatertubes in the one radiant heating section. The hydrocarbon fluid is'firstpassed through a group of wall heater tubes in the radiant heatingsection which are spaced relatively far apart so that a large amount ofheat per unit of heating surface is added to the hydrocarbon fluidpassing through the first group of Wall heater tubes. The heatedhydrocarbon fluid is then passed through another group of Wall tubes andpart of an exposed row of roof tubes. In the second group of heatertubes, the tubes are spaced closer together than the tubes in the firstgroup to reduce the amount of heat per unit of heating surface beingadded to the hydrocarbon fluid passing through this second group ofheater tubes.

The heated hydrocarbon fluid is then passed through a third group ofheater tubes which includes an exposed row of roof tubes. Thetubes inthis third group are spaced further apart than the tubes in the secondgroup and are spaced at distances about equal to the distance betweentubes in thefirst group. The hydrocarbon fluid passing through the thirdgroup is further heated but at a slower rate than the rate of heating ofthe hydrocarbon fluid passing through the first and second groups. Thisrate of heating is lower than the rate of heating of the first group forthe reason that there is a second row of roof tubes behind the thirdgroup as will be presently described.

The heated hydrocarbon fluid leaves the third group of tubes and passesthrough a fourth group of tubes which comprises part of the exposed rowof roof tubes. The third and fourth groups of tubes are in the samehorizontal plane and form the exposed row of roof tubes. These tubes inthe fourth group are closer together than those in the third group andare spaced at about the same distance from each other as the'tubes'inthe second group of tubes above described. In the fourth groupthehydrocarbon fluid is further heated but at a slower rate than the rateof heating of the hydrocarbon fiuid passing through the third group forthe reason that the heater tubes in the fourth group are spaced closertogether and there is also a shielded row of roof tubes behind thisfourth group of heater tubes.

The hydrocarbon fluid after passing through the fourth group of tubes ispassed toa fifth group of tubes which comprises a shielded row of rooftubes arranged behind the roof tubes forming the third group abovedescribed. The heater tubes in the fifth group are spaced apart at aboutthe same distances as the heater tubes in the thirdgroup but as they areshielded they receive less heat per unit of heating surface than thehydrocarbon fluid passing through the exposed row of tubes in the thirdgroup. In passing through the fifth group the hydrocarbon fluid has itstemperature further raised a small amount.

The heated hydrocarbon fluid then passes through a sixth group of heatertubes which forms part of the shielded second row of roof tubes. Theheater tubes in the sixth group are spaced closer together than thetubes in the fifth group and are spaced at about the same distances fromeach other as the tubes in the fourth group. In addition the heatertubes in the sixth group are placed or positioned closer to the exposedrow of roof tubes comprising the fourth group and farther from the roofof the furnace than the fifth group of tubes. Due to the positioning inthe sixth group the amount of heat per unit of heating surface added tothe hydrocarbon fluid passing through these heater tubes is reduced andthe hydrocarbon fluid is maintained at substantially the sametemperature during its passage through the sixth group of heater tubes.The sixth group of heater tubes comprises a soaker section in whichconversion of the hydrocarbon fluid is mainly carried out. r

In the drawing the figure represents a transverse vertical cross sectiontaken through a heating apparatus embodying one form of my invention.

character I0 designates a furnace or heating apparatus including radiantheating section i2, radiant heating section l4 and a convection heatingsection It. The radiant heating sections are each separately fired bymeans of burners 23 which burn fuel, such as gas, to supply radiant heatto the radiant heating sections. The burners are preferably arranged inthe lower portion of each radiant heating section. The radiant heatingsections communicate at their one end and the products of combustionfrom each radiant heating section pass upwardly through the commonconvection heating section It which is positioned above the centralportion ofthe' furnace and which communicates with the radiant heatingsections at their communicating ends. If desired, the convection heatingsection may be arranged in other positions, for example, it may bearranged between the radiant heating sections or at an end of thefurnace.

While I have shown a furnace provided with two radiant heating sectionsand a common convection section I do not wish to be restricted in thisrespect as my invention may be employed with other types of furnaces andmay be used in a heating apparatus including a single radiant heatingsection and preferably a convection heating section.

The heating apparatus shown in the drawing is a box-type furnace inwhich each radiant heating section has a roof 22, side walls 24, floor26 and end walls 28. The burners in each radiant heating sectionpreferably extend through opposite end walls 28 of the furnace so thatthe flames from opposite burners are directed toward each other. Or theburners in one end wall may be ofiset with respect to the burners in theopposite'end wall.

In describing my invention reference will be made to one radiant heatingsection as the radiant heating sections are substantial duplicates whenseparate streams of .hydrocarbon fluids of substantially the samecomposition are to be treated and the description Referring now to thedrawing the reference of one radiant heating section will suflice forboth sections. The heater tubes in each radiant heating section arehorizontally arranged in vertical and horizontal rows adjacent theboundary surfaces of the radiant heating section and the heater tubesextend longitudinally of the furnace. The ends of the tubes areconnected by suitable headers (not shown) which are positioned in headerboxes (not shown) so as to provide a heating coil for the hydrocarbonfluid to be heated.

The convection heating section i6 is provided with two groups of heatertubes 32 and 34 for preheating separate streams of hydrocarbon fluid,one stream passing to one radiant heating section 12- and the otherstream passing to the other radiant heating section 14.

The heating of one stream of hydrocarbon fluid will now be described.When it is desired to convert hydrocarbons such as gas oils to lowerboiling hydrocarbons such as motor fuels and with burnershaving a knowncapacity, my invention may be usedto so arrange and space the heatertubes to effect controlled heating of the hydrocarbons without danger ofoverheating and consequent deposition of carbon in the tubes. The tubesare so arranged in groups that the hydrocarbons are first subjected torapid heating and then the rate of heating. is decreased until atthe endof the conversion operation only sufficient heat is added .to thehydrocarbons to effect the desired extent of conversion. I accomplishthese results by proper spacing and grouping of the tubes in single anddouble rows. In the specific form of the invention six different ratesof heating are utilized .to heat and convert hydrocarbons.

Hydrocarbon fluid to be heated is passed through line 38 by pump 39 andthrough the heater tubes 34 in the'convection heating section [6 wherethe hydrocarbon fluid ispreheated. The preheated hydrocarbon fluid isthen passed through line.40 and. introduced into the lowest tube 42 of.the first group of wall heater tubes designated asI in the drawing. Thehydrocarbon fluid passes through tubes in group I which begins with tube42 and ends with tube 43.

In this-form of the invention there is a single row of wall heater tubeswhich are substantiallyequidistantly spaced at relatively largedistances whereby the hydrocarbon fluid passing through these tubes israpidly raised in temperature. As the tubes are relatively far apart,the areas of the boundary surface between the tubes become heated andreradiate heat to the tubes.

The heated stream of hydrocarbon fluid is then passedthrough a secondgroup of heater tubes designated as II on the drawing. This second groupof tubes includes wall heater tubes 44, 46, 48,50 and 52 which arepositioned adjacent the side wall, 24,0f the radiant heating section 12and in the upper portion of the radiant heating section [2. .Group IIalso includes roof tubes 54 and 55 adjacent, an upper corner of theradiant heating section l2 which form a single row of roof tubes andwhich are spaced apart at about the same distances as the wall heatertubes 44, 46, 48, 50 and 52 of the second group. In the heater tubes ofgroup II the hydrocarbon fluid is further heated but the rate of heatingis reduced for the reason that the heater tubes are spaced closertogether than the heater tubes in the group I. a The heater tubes ingroup II are substantially equidistantly spaced. r

The stream of hydrocarbon fluid is then passed through groups of rooftubes which are arranged in a double row and is further heated. Theheated stream ofhydrocarbon fluid first passes through certain tubes inan exposed row of roof tubes forming a group designated as III on thedrawing in which the individual roof tubes are substantiallyequidistantly spaced apart about the same distances as those in group I.However, due to the fact that there is a second row of roof tubes behindthe exposed row of roof tubestheamount of heat per unit of heatingsurface added to the hydrocarbon fluid passing through tubes in groupIII is less than that added to the hydrocarbon fluid passing throughtubes in group I. The first tube in group III is Eli and the last tubeis 62.

The heated hydrocarbon fluid is then passed through another group oftubes comprising the remaining exposed roof tubes and which isdesignated as group IV in the drawing. The'first tube in group IV is 64and the last tube is 66. In group IVthelast tube 66 is adjacent theconvection heating section l6. In the specific form of the inventionthere are more tubes in group IV-than in the previous groups abovedescribed.

The tubes in this group are substantially equidistantly spaced but theyare spaced closer together than the tubes in group III. The heater tubesin groups III and IV form the exposed row of roof tubes and the tubesare substantially in the same horizontal plane and in alinement. Due tothe closer spacing of the heater tubes and due to-the presence of a rowof tubes behind the heater tubes in group IV the rate of heating of thehydrocarbon fluid passing through these tubes is further decreased. 1

- The heated hydrocarbon fluid leaving group IV of heater tubes is thenpassed through line 68 and isintroduced into the first tube 70 of theshielded row of roof tubes designated as group V in the drawing andpasses through these tubes. The last tube in this group is tube 12. Thefirst tube in group V isarranged in the upper portion of radiant heatingsection l2 adjacent the corner distant from the convection heatingsection I6. The heater tubes in group V are positioned behind the heatertubes in group III previously described. The heater tubes in group V aresubstantially equidistantly spaced at about the same distances apart asthe heater tubes in group III but the tubes are staggered with respectto the tubes in group V. It is to be noted that the first or shieldedroof tube H! of group V is positioned at some distance from the sidewall 24 so that the roof tubes 54 and 56 forming part of group II iabove described do not have a shielded row of roof tubes behind them.

After being heated in the heater tubes in group V'the hydrocarbon fluidis passed through the second shielded row of roof tubes indicated asgroup VI on the drawing. Group VI starts with roof tube M and ends withroof tube 76. End tube It is positioned to the rear of tube 65 in groupIV'and is adjacent the convection heating section l6. The heater tubesin group VI are substantially equidistantly spaced but they are arrangedcloser together than the heater tubes in group V and in the specificform of the invention the heater tubes in group VI are also arrangedcloser to the exposed row of roof tubes IV and" fartherfrom the roof 22than the tubes in group V.

Also the number of tubes in group VI is larger than'the number of tubesin each of groups I, II, III- and V but the same as the number of tubesin group IV. Group VI is arranged behind group IV and the tubes of eachgroup are in staggered relation. With this arrangement and number oftubes the rate of -heating of the hydrocarbon fluid passing through theheater tubes in group VI is further reduced. The heater tubes form inggroup VI comprise a soaking section in which less heatis supplied to thehydrocarbon fluid being converted and the temperature of the hydrocarbonfluid is maintained substantially constant to efiect the desired extentof conversion without objectionable coking and without changing thefiring of the burners. The products of conversion leave the last heatertube 16 in the group VI and pass through line 18 from the furnace. Fromthe above it will be seen that the hydrocarbon is heated in groups oftubes in one radiant heating section and the control of heating isobtained by arranging and spacing the tubes.

In the heatingof the hydrocarbon fluid as it passes through radiantheating section I2, the hydrocarbon fluid passes generally upwardlythrough tubes in groups I and II, then generally from leftto the rightthrough groups III and IV as viewed'in the figure and then generallyfrom left to right-through groups V and VI as viewed in the figure; 1

A specificexample of heating a hydrocarbon fluid and the arrangement ofthe heater tubes -will now be given. All the heater tubes are about 5inches in outside diameter and about 4 inches in inside diameter. About750 barrels per hour of a Mid-Continent gas oil under a pressure ofabout 1000 pounds per sq. in. and at a temperature of about 660 F. arepassed through line 38 and through the one set of convection heatingtubes .34 to preheat. the hydrocarbon fiuidto about 'FZ85...F. While .Ihave given specific temperatures and pressures in the specific example,it is to beunderstood that these are by way of illustration only and thetemperatures and pressures. may be varied for the same stock or fordifferent stocks. .I-Iigher or lower temperatures and higher or lowerpressures may be used.

The heated hydrocarbon fluid is then passed through line 40 and upwardlythrough group I of wall heater tubes wherein it is subjected to drasticheating and the temperature of the hydrocarbon fluid is raised to about831.F. In the particular form of the invention shown in the drawingthebottom wall heater tube 42 is spaced about 6 :from the floor 26 ofthe "furnace. The wall heater. tubes in group I are about. 137/ apart,center to center, and are spaced about 5%" from the side wall 24. Theheat density or rate of heat transfer to group I of heater tubes isabout 22,050 B. t. u./hr./sq. ft. The'hydrocarbon fluid after passingthrough the heater tubes in group I is passed through the heater tubesforming group II wherein the temperature is raised to about 865 F. Thewall heater tubes indicated as 44, 46, 48, 50 and 52 on the drawing arespaced apart about 9%.", center to center; and the vertical row of thesetubes is spaced'about 5 from the side wall 24. In group II there arealso included roof tubes 54 and 56 which are spaced apart about 9%.",center to center, and about 18"'from the roof 22. Tube 52 isalso spacedabout 9%", center to center, from roof tube 54 and about 18 from roof22. It is to be noted that there are no roof tubes directly behind rooftubes 54 and 56. Due to the closer spacing of the heater tubes in groupII the rate of heating of the hydrocarbon fluid in the heater tubes isreduced. The heat density or rate of heat transfer to the tubes'of groupII .is about 17,820 B. t. u./hr./sq. ft. i

The hydrocarbon fluid after leaving the heater tubes in group II ispassed through the, exposed row of roof tubes in group III and thetemperature of the hydrocarbon fluid is;r aisedito about 895 F. Theheater tubes in group III are. about 13% apart, center to center, and.therate of heat transfer or heat density is about 16,600 E. t.u./hr./sq. ft. The heater tubes in group III are aboutlS" from the roof22 and about .12? from the shielded row of roof tubes forming roup V.

The heated hydrocarbon fluid is then passed through the heater tubes ingroup IV which are spaced apart about 9%,", center to center, and thehydrocarbon fluid is heated to about 926 F. The heat density or rate of.heat-transfer tothis group of tubes is about 14,130 B. t. u./hr./sq. it.The heater tubes in group IV are about 18" from the roof 22 and about 8"from'the shielded row of roof tubes forming group VI.

The heated hydrocarbon fluid leaves group IV of tubes through line 68and is .then. passed through group V comprising the shielded row of rooftubes. Group V is positioned behind group III. The tubes in group V areabout13'V apart, center to center, and are about 6" from the roof 22 ofthe furnace and about 12" from the exposed row of roof tubes forminggroup III. The heat density or rate of heat transfer to the shielded rowof roof tubes forming group V is about 10,950 E. t. u./hr./sq. ft.

The hydrocarbon fluid after being heated to about 939 F. in the heatertubes in group V is passed through the shielded row of roof tubesforming group VI wherein the temperature of the hydrocarbon fluid ismaintained substantially constant. The heater tubes in group VI arearranged closer together than the tubes in group V. The tubes in groupVI are about 9 apart, center to center, and the heat density or rate ofheat transfer is about 5,300 B. t. u./hr./sq. ft. The heater tubes ingroup VI are arranged closer to the exposed row of roof tubes than thetubes in group V. The heater tubes in group VI are about 8" away fromthe exposed row of roof tubes in group IV and about 10" away from theroof 22.

'In the specific form of the invention shown in the drawing the distancebetween tube 43 of group I and tube 44 in group II is about 16". Thedistance between tube 56 of group II and tube 60 of group III and thedistance between tube 62 of group III and tube '64 of group IV are aboutthe same, namely 13%". The distance between tube 12 in group V-and tube14 in group VI is about 14 The heated hydrocarbon fluid leaves theheater tubes in group VI through line 18 at a temperature of about 940F. and under a pressure of about 750 pounds per sq. in. From this itwill be seen that the heater tubes in group VI form a soaking sectionwherein the temperature of the hydrocarbon fluid being heated ismaintained substantially constant but a relatively small amount of heatis added to the hydrocarbon fluid in order to carry out the conversionreaction. In the first groups of heater tubes the rate of heating wascontrolled to rapidly raise the temperature of the hydrocarbon fluid toa conversion temperature. The hydrocarbon fluid at conversiontemperature is passed through group VI as a soaking section, and thesoaking section is provided to supply suflicient heat to the hydrocarbonfluid to effect the desired extent of conversion without depositingappreciable amounts of carbon or coke in the tubes- The heater tubesinthe second radiant heating section M are arranged similarly to theheater tubes in radiant heating. section [2 and the description of theheating of hydrocarbon fluid passing through the heater tubes in theconvection heating section [6 and radiant heating section I2 alsoapplies to the heating of the Other stream passing through the heatertubes 32in convection heating section It and through the groups of walland roof heater tubes arranged in the other radiant heating section [4.

While I have shown one form of heating apparatus embodying my inventionit is to be understood that this is by way of illustration and variousmodifications and changes may be made Without departing from the spiritof my invention. I

I claim:

l. A heating apparatus for heating hydrocarbon fluids to conversiontemperature including a radiant heating section, means for supplyingradiant heat thereto, groups of heater tubes arranged adjacent boundarysurfaces of said radiant heating section, certain of said heater tubesbeing arranged in a double row comprising an exposed row and a shieldedrow, means for passing hydrocarbon fluid to be heated through saidgroups of heater tubes in succession, the first groups of tubes beingarranged in a single row, the tubes in each of said first groups beingsubstantially equidistantly spaced and the tubes in said first groupbeing spaced apart at greater distances than the tubes in another group,the remaining groups of tubes forming the double row of tubes, certaingroups forming the exposed row and certain other groups forming thshielded row, the tubes in each of the groups of said double row beingsubstantially equidistantly spaced and the tubes in certain groups beingspaced at greater distances apart than the tubes in other groups oftubes, to control the rate of heating of the hydrocarbon fluid passingthrough said tubes, the last group of tubes in said shielded row beingspaced further from the boundary surface than the adjacent group oftubes in said shielded row, the last group of tubes in said shielded rowforming a soaking section, the rate of heating the hydrocarbon fluidpassing through said tubes in the groups decreasing from the first tothe last group.

2. A heating apparatus for heating hydrocarbon fluid to conversiontemperature including radiant heating sections and a convection heatingsection adapted to receive combustion products from said radiant heatingsections, heater tubes in said convection heating section for preheatingstreams of hydrocarbon fluid, fuel burning means for supplying radiantheat to said radiant heating sections, heater tubes arranged adjacentboundary surfaces of each of said radiant heating sections, means forpassing separate streams of hydrocarbon fluid through said heater tubes,said heater tubes in each radiant section being arranged and spaced tocontrol the rate of heating of the hydrocarbonfluid passingtherethrough, said heater tubes in each radiant heating section beingarranged in groups with certain of the heater tubes being arranged in asingle row and other tubes being arranged in a double row comprising anexposed row and a shielded row, said heater tubes in each of the groupsin the single row being substantially equidistantly spaced and the tubesin one group be ing spaced difierently from the tubes in another groupto obtain different heating rates, said heater tubes in the double rowin each radiant heating section being in pairs of groups, the groups inone row being behindthe groups in the other row, said heater tubes ineach pair of groups being substantially equidistantly spaced and thetubes in one pair of groups being differently spaced from the tubes inanother pair of groups, one group of tubes in said shielded row in eachradiant heating section being arranged further away from its adjacentboundary surface than the other group in said shielded row.

3. A heating apparatus for heating hydrocarbon fluid to conversiontemperature including a radiant heating section, means for supplyingradiant heat to said radiant heating section, heater tubes arrangedadjacent boundary surfaces of said radiant heating section, means forpassing hydrocarbon fluid through said heater tubes, said heater tubesbeing arranged and spaced to control the rate of heating of thehydrocarbon fluid passing therethrough, said heater tubes being arrangedin groups with certain of the heater tubes being arranged in a singlerow and other tubes being arranged in a double row comprising an exposedrow and a shielded row, said heater tubes in each of the groups in thesingle row being substantially equidistantly spaced and the tubes in onegroup being spaced difierently from the tubes in another group to obtaindifferent heating rates, said heater tubes in the double row being inpairs of groups, the groups in one row being behind the groups in theother row, said heater tubes in each pair of groups being substantiallyequidistantly spaced and the tubes in one pair of groups beingdifferently spaced from the tubes in another pair of groups, one groupof tubes in said shielded row being arranged further away from itsadjacent boundary surface than the other group in said shielded row.

JOHN HERMAN RICKERMAN.

